Extreme Networks' Ethernet Automatic Protection Switching (EAPS) Version 1
RFC - Informational
(October 2003; No errata)
No shepherd assigned
RFC 3619 (Informational)
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Network Working Group S. Shah
Request for Comments: 3619 M. Yip
Category: Informational Extreme Networks
Ethernet Automatic Protection Switching (EAPS)
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document describes the Ethernet Automatic Protection Switching
(EAPS) (tm) technology invented by Extreme Networks to increase the
availability and robustness of Ethernet rings. An Ethernet ring
built using EAPS can have resilience comparable to that provided by
SONET rings, at a lower cost and with fewer constraints (e.g., ring
Many Metropolitan Area Networks (MANs) and some Local Area Networks
(LANs) have a ring topology, as the fibre runs. The Ethernet
Automatic Protection Switching (EAPS) technology described here works
well in ring topologies for MANs or LANs.
Most MAN operators want to minimise the recovery time in the event
that a fibre cut occurs. The Ethernet Automatic Protection Switching
(EAPS) technology described here converges in less than one second,
often in less than 50 milliseconds. EAPS technology does not limit
the number of nodes in the ring, and the convergence time is
independent of the number of nodes in the ring.
Shah & Yip Informational [Page 1]
RFC 3619 Extreme Networks' EAPS October 2003
2. Concept of Operation
An EAPS Domain exists on a single Ethernet ring. Any Ethernet
Virtual Local Area Network (VLAN) that is to be protected is
configured on all ports in the ring for the given EAPS Domain. Each
EAPS Domain has a single designated "master node". All other nodes
on that ring are referred to as "transit nodes".
Of course, each node on the ring will have 2 ports connected to the
ring. One port of the master node is designated as the "primary
port" to the ring, while the other port is designated as the
In normal operation, the master node blocks the secondary port for
all non-control Ethernet frames belonging to the given EAPS Domain,
thereby avoiding a loop in the ring. Existing Ethernet switching and
learning mechanisms operate per existing standards on this ring.
This is possible because the master node makes the ring appear as
though there is no loop from the perspective of the Ethernet standard
algorithms used for switching and learning. If the master node
detects a ring fault, it unblocks its secondary port and allows
Ethernet data frames to pass through that port. There is a special
"Control VLAN" that can always pass through all ports in the EAPS
Domain, including the secondary port of the master node.
EAPS uses both a polling mechanism and an alert mechanism, described
below, to verify the connectivity of the ring and quickly detect any
2.1. Link Down Alert
When a transit node detects a link-down on any of its ports in the
EAPS Domain, that transit node immediately sends a "link down"
control frame on the Control VLAN to the master node.
When the master node receives this "link down" control frame, the
master node moves from the "normal" state to the ring-fault state and
unblocks its secondary port. The master node also flushes its
bridging table, and the master node also sends a control frame to all
other ring nodes, instructing them to flush their bridging tables as
well. Immediately after flushing its bridging table, each node
begins learning the new topology.
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RFC 3619 Extreme Networks' EAPS October 2003
2.2. Ring Polling
The master node sends a health-check frame on the Control VLAN at a
user-configurable interval. If the ring is complete, the health-
check frame will be received on its secondary port, where the master
node will reset its fail-period timer and continue normal operation.
If the master node does not receive the health-check frame before the
fail-period timer expires, the master node moves from the normal
state to the "ring-fault" state and unblocks its secondary port. The
master node also flushes its bridging table and sends a control frame
to all other nodes, instructing them to also flush their bridging
tables. Immediately after flushing its bridge table, each node
starts learning the new topology. This ring polling mechanism
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